1. Field of the Invention
The present disclosure relates to an availability prediction method for a high availability cluster, and more particularly, to a method for predicting an availability of a high availability cluster, which can determine an optimal number of nodes meeting a predetermined required availability level and a method for operating the same.
This work was supported by the IT R&D program of MIC/IITA [2007-S-016-01, A Development of Cost Effective and Large Scale Global Internet Service Solution]
2. Description of the Related Art
Generally, a cluster system refers to a system for integratedly managing a virtual image program by grouping a plurality of nodes having the similarity therebetween.
Many researches in various fields such as high availability (HA), load-balancing, high performance computing and grid computing are in progress. Especially, the high availability is an important aspect of a cluster technology for providing services without a failure upon a user's request in today's Internet environment.
A high availability cluster includes one or more nodes to prepare for a failure on any node of them. Moreover, the high availability cluster checks, at any time, a state of an individual node to dynamically remove a failed node in the cluster, allows other nodes to perform a corresponding task in behalf of the failed node, and allows a recovered node to join the cluster again.
FIG. 1A is a block diagram illustrating a configuration of a related art asymmetric cluster system.
Referring to FIG. 1A, the asymmetric cluster system 100 includes a head node 110, a switch node 120, and a compute node 130. The head node 110 monitors the compute node 130. The switch node 120 is placed between the head node 110 and the compute node 130. The compute node 130 fulfills a user's request by the head node 110.
The head node 110 distributes cluster-related software, monitors a failure on the compute node 130, and recovers the failed node to optimal system availability. It is very important to minimize failures of the nodes in the practical operation of the cluster system.
The head node 110 includes two Ethernet devices. One fulfills a user's request through a private network connected to the compute 130 via the switch 120, and the other fulfills the user's request through a public network.
The switch 120 provides the head node 100 with a path to the compute node 130 by being connected with the private network.
The compute node 130 carries out a certain operation according to a command of the head node 100 by being connected with the private network.
FIG. 1B is a block diagram illustrating a configuration of a related art high availability cluster system.
Referring to FIG. 1B, the high availability cluster system includes two head nodes 211 and 212, two switches 221 and 222, m number of compute nodes 230_1 to 230—m. 
The head nodes 211 and 212 are duplexed. Accordingly, when one of the head nodes 211 and 212 is failed, the failed node may be replaced with the other node.
In this case, since two switches 221 and 222 are used, each of the head nodes 211 and 212 includes three Ethernet devices.
FIG. 2 is a block diagram illustrating a configuration of a general high availability cluster system.
Referring to FIG. 2, the high availability cluster system includes a plurality of head nodes 250_1 to 250—n, a plurality of switches 260_1 to 260_1, a plurality of compute nodes 270_1 to 270—m. “Number of nines”, which is a value indicating availability, varies with the number n of the head nodes 250_1 to 250—n. 
The availability value varies with the number n of the nodes, the number of active and passive nodes, or a configuration of the nodes (e.g., where the cluster system may be constituted of only head nodes, or the head nodes and the switches nodes).
The larger is the number of nodes, the higher is availability probability of the high availability cluster system. However, since there is a limitation to the number of the nodes, it is necessary to design a system in consideration of the availability probability in accordance with the number of the nodes prior to the system construction.